Cell had this to say about a USSJ, "Yes, it is a magnificent power, greater than mine by a wide margin, but power isn't everything."
Again, prove that Superman can accelerate to light speed as fast as SSJ2, or even SSJ1 Goku.
Goku in his first transformation to Super Saiyan moved four feet before a beam traveling at 80/175 the speed of light could travel 5 inches.
Imagine how fast even a full power Super Saiyan moves.
Second HAHAHAHAHHHAHAHAH I cant believe you think Ultimate Super SaiyanJin 1 is stronger then Super Saiyanjin 3. Omg dude you simply dont stop to amuse me. Goku himself state in the Chamer(can't spell) that he need a form where he has the same strenght like USSJ, but to hold his speed and not let it get slower.
Just because he needed that form doesn't mean SSJ2 was the form, you have to remember that Gohan was stronger than Goku after their training in the room of spirit and time, as stated by Goku.
USSJ is by far the strongest Saiyan Power Up, it's a brick house, and Superman couldn't kill it with one punch, he could out power it, but he couldn't kill it, and Superman, if he was pissed off enough couldn't hit Goku SSJ3 at the end of the DBZ Manga, maybe when he first transformed, but not at the end.
I believe that Broly is what a USSJ would be like in combat.
Prove that Superman won't get disoriented fighting two completely deferent power houses that use two completely deferent types of strengths, one, strength, two, speed.
Goku doesn't have to pound Superman to death, just get him confused and angry enough to leave himself open for a Super Kamehameha from an SSJ3.